i respectfully disagree. there are things in a professional kitchen that benefit from the mid-sized knife. a lot of people call them line knives and that is a great description. they are great for working a line when you dont want to have your whole kit handy. i personally do not care to use my 270mm gyuto on the line (once a month when i actually work it) because it is too big. i need something with more finesse. a 150mm does not have the ability to slice some things that we do to order. this makes it a great option to have. i would also like to note that in the past year i have become a minimalist and understand where you are coming from, i just think there is a use for this particular knife.
also i found that it would work very well for my daily jobs which is mostly fabrication of whole proteins (mostly fish, pig, lamb, and goat). my mioroshi deba does okay with some things like spanish mackerel or jon dory but i think a 210mm might fit the bill a little better.